Air Distribution Engineering Guide

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Engineering Guide Air Distribution

S E C T I O N E G

Please refer to the Price Engineer’s HVAC Handbook

for more information on Air Distribution


http://slidepdf.com/reader/full/air-distribution-engineering-guide 2/19EG-2All Metric dimensions ( ) are soft conversion . © Copyright Price Industries Limited 2011.Imperial dimensions are converted to metric and rounded to the nearest millimetre.

Air DistributionEngineering Guide

Space Air Diffusion

Proper selection of air diffusion devicesrequires basic knowledge of the mechanicsof room air distribution. Figures 1 and 2illustrate the interactions of the majorfactors influencing room air distribution.

Primary AirPrimary air is defined as the conditionedair discharged by the supply outlet. Thisair provides the motive force for room airmotion.

Total AirTotal air is defined as the mixture of primaryair and entrained room air which is underthe influence of supply outlet conditions.This is commonly considered to be the airwithin an envelope of 50 fpm [0.25 m/s] (orgreater) velocity.The temperature differencebetween the total air and the room aircreates buoyant effects which cause coldsupply air to drop and warm air to rise.

ThrowThrow is the distance from the centerof the outlet face to a point where thevelocity of the air stream is reduced toa specified velocity, usually 150 [0.75],100 [0.50] or 50 fpm [0.25 m/s] (Figure 3).These velocities are referred toas terminal velocity and thereforeindicated as T150 [T0. 75], T100 [T0.50],T50 [T0 .25] r espectively. Throw isprimarily a function of mass flow andoutlet velocity and therefore can be

reduced by decreasing either of thesevalues.

Drop

The drop of cool total air, as shown inFigure 1,is the result of vertical spread of the airstream due to entrainment of room air,and the buoyancy effect due to the densitydifferences between the total air packageand the surrounding primary room air. Theterm density is very important as drop isprimarily dependent upon the mass flowof the total air. Drop can be minimized byspreading air uniformly over the ceilingsurface, thus reducing the mass flow perunit surface area.

Spread

The spread of an outlet is defined as thedivergence of the air stream in a horizontalor vertical plane and is a function of theoutlet geometry (Figure 3).

Surface EffectDrop can also be effectively reduced byuse of the surrounding ceiling surface.When supply air velocity is sufficientlyhigh, a negative or low pressure area iscreated between the moving air mass andthe ceiling at or near the supply air outlet.This low pressure area causes the movingair mass to cling to and flow close to theceiling surface. This principle is known asthe Coanda effect. See Chapter 2—FluidMechanics in the Price Engineer's HVAC

Figure 1: Space air diffusion with overhead cooling

Figure 2: Space air diffusion with overhead heating

221 / 2°Deflection

S p r e a d ,

F e e t

22½º

22½º

0º

10

5

0

5

100 10 20 30 40

Throw, Feet

50 fpm

150 fpm

Typical 100 fpm

Envelope

Figure 3: Throw/spread

Handbook for a more detailed explanation.Good air distribution design makes use ofroom surfaces to help keep the supply airoutside the occupied zone.

Occupied ZoneThe occupied zone is usually defined as thearea within 6 ft [1.8 m] of the floor and notwithin 1 ft [0.3 m] of the boundaries of thespace (walls, etc.). As this is the area of

occupancy, it is desirable to avoid excessivedraft velocities and temperature differenceswithin this space.

Stagnant Air

InducedRoom Air

Primary Air

6 ft [1.8 m]

0Temperature

Total Air

Coanda Effect

OccupiedZone

H e i g h t , f t [ m ]

R E

T U R N

SUPPLY

N a t u r a l C o n v e c t i o

n

Throw

D r o p N

a t u r a l C o n v e c t i o n

Primary Air

6 ft [1.8 m]

0Temperature

Total Air

Coanda Effect

OccupiedZone H

e i g h t , f t [ m ]

RETURN

Induced

Room Air

SUPPLY


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Imperial dimensions are converted to metric and rounded to the nearest millimetre.

Throw

Throw is, by definition, the distance the air

is projected out from the center of the outletface. When discussing throw, we mustreference it to a specific air velocity, whichis called the terminal velocity. Most often,throw is referenced to terminal velocitiesof 150 [0.75], 100 [0.50] and 50 fpm [0.25m/s]. These velocities are indicated asT150 [T0.75], T100 [T0.50] and T50 [T0.25]respectively. Throw is primarily a functionof the air volume being discharged by theair outlet and the induction rate of the airoutlet. The throw can therefore be reducedby decreasing the air flow from the outletor by selecting an air outlet with a highinduction rate.

Room air movement is created by its gradualinduction toward the primary and total airstreams. It is this constant mixing thatprovides the mechanisms for heat transferbetween the supply and room air. Whenair movement does not occur (usually as aresult of insufficient outlet velocities or pooroutlet location), a stagnant layer of roomair is formed. Above that layer (or below inthe case of overhead heating), proper heattransfer does not exist and temperaturestratification occurs. This is illustrated bythe temperature gradient curves shown inFigure 2. It is always desirable to keep thestagnation layer above the occupied zone incooling and as near to the floor as possible

when heating from above.Convection Currents

The total air package can easily beinfluenced by several factors within thespace. One of these factors that occurs inexterior zones of buildings is the naturalconvection currents resulting from a hotoutside wall during cooling (Figure 1) or acold outside wall during heating (Figure 2).The upward movement of air in the vicinityof the hot surface tends to oppose the totalair movement in overhead cooling. Thiscan act to reduce the outlet throw valuesor even cause the colder total air to leavethe ceiling and create drop into the space.The downward movement of cold air inthe vicinity of a cold surface (Figure 2)

can create cold drafts within the occupiedspace. In the case of overhead heating, theonly effective way to minimize these draftsis to direct a high velocity jet of warmair over the wall surface to reduce thedifference between the temperature of thesurface and that of the room air. Maintainingsurface temperatures as close to the space

Selection Fundamentals - Performance Factors

Air Pattern

Air outlets are available with a variety of

air pattern options. Some ceiling diffuserscan be selected with either a 1, 2, 3 or 4way horizontal pattern (Figure 4). Thelayout of the room and available locationof the diffuser determines which pattern isselected. Some ceiling outlets also offer avertical pattern option for high ceiling orheating applications. Plenum slot diffusersare often available with 1 or 2 way horizontalas well as vertical air pattern. Sidewall grillescan be set for straight or spread pattern,while linear bar grilles are available in severalangular pattern options.The performance ofthe air outlet and the resultant comfort levelin the space are greatly influenced by thetype of air pattern selected.

Stratification

Mixing ventilation systems generally supplyair in a manner such that the entire roomvolume is fully mixed. The cool supply airexits the outlet at a high velocity, inducingroom air to provide mixing and temperatureequalization. Since the entire room is fullymixed, temperature variations throughoutthe space are small. See the temperaturegradient curve in Figure 1. This variation inroom air temperature from floor to ceilingis known as stratification. When warm airis introduced with a ceiling diffuser, somestratification can be expected due to thelower density of the warm supply air (seetemperature gradient curve in Figure 2).

If the stratification can be limited to occurabove the occupied zone, it is not of concernfrom a comfort standpoint. Stratificationin the occupied zone must be limited inaccordance with ASHRAE Standard 55. SeeChapter 4—Indoor Environmental Qualityin the Price Engineer's HVAC Handbookfor an explanation of how temperaturestratification affects comfort.

Room Air

Finally, we come to the medium throughwhich all metabolic heat transfer occursand therefore is the most critical factor incontrolling human comfort - the room air.The room air consists of all the other airwithin the space which is not included in

the total air package. Proper air distributionattempts to condition the room air tomaintain draft velocities and temperatureswithin the comfort range as defined inChapter 4—Indoor Environmental Quality inthe Price Engineer's HVAC Handbook. Thisvelocity of air within the occupied zone isknown as Room Velocity.


Space Air Diffusion

GREEN TIP

Location of supply and return outletsto eliminate short circuiting willincrease the ventilation effectiveness.

as possible also minimizes radiation heattransfer potential between the surfaceand the occupants, resulting in improvedcomfort response. Note that increasing theperimeter surface temperature will alsoincrease the building heat loss and shouldbe considered in the load calculations.

Return

The return air inlet has very little effect onroom air diffusion, regardless of inlet type olocation. However, return air inlets should belocated a sufficient distance from the supplyoutlet so that short-circuiting of supply aidoes not occur. It may also be desirable tolocate the returns in the stagnant zone toremove unwanted warm or cool air. Fo

cooling, a high sidewall or ceiling return wilremove warm air from the space (Figure 1)For heating a low sidewall return will removewarm stagnant air (Figure 2).

Drop

Whenever cool supply air is introduced into

a warmer space its natural tendency will bedownward movement.The vertical distancewhich the air jet extends below the ceilingis called the drop (Figure 5). Similar to thethrow, we discuss the drop referenced to aspecific terminal velocity. For simplicity weuse the same three terminal velocities asfor throw: 150 [0.75], 100 [0.50] and 50 fpm[0.25 m/s]. If the supply air projects into theoccupied space uncomfortable drafts wiloccur. Drop can be minimized by utilizing thesurface effect of the ceilings. Outlets locatedin or near the ceiling will exhibit less dropthan outlets located on exposed ductworkTypically, the drop will increase as the aivolume, and subsequently the outlet throwis increased. The vertical spread of the air je




increases with distance travelled. Reducingthe supply air volume and increasing thesupply air temperature will reduce the drop.One caution regarding reducing air volumetoo low is that the air jet may detach fromthe ceiling and fall into the occupied zone.This condition is known as 'dumping' andshould be avoided.

Spread

Spread is the horizontal width of the air jet being discharged by the air outlet.Delivering the air in a spread pattern tendsto reduce both the throw and the drop of anair outlet. As with the throw and drop, thesame three terminal velocities are used todiscuss spread: 150 [0.75], 100 [0.50] and 50

fpm [0.25 m/s]. Dissipating the air streamover a wider area increases entrainment andreduces the mass flow per unit surface area(Figure 5).

Pressure Drop

Every air outlet produces a pressure losswhen air is passed through it. The magnitudeof the pressure loss will vary dependingon the model, size and geometry of theair outlet, and is measured in in. w.g. [Pa].Pressure drop will increase proportionallywith air flow. The pressure drop of the airoutlet must be taken into account whencalculating the system pressure whenselecting the supply fan.

Noise Level

Typically, the noise level of an air outletis rated with a Noise Criteria (NC) soundpressure value based on an industrystandard 10 dB default for room absorption.This NC value assumes an average roomand approximate distance of 5 ft [1.5 m] froma single source. For a detailed explanationof the NC rating method see Chapter 7—Basics of Acoustics in the Price Engineer'sHVAC Handbook.

An air outlet's noise level (NC rating) isdirectly proportional to the air volumesupplied through the outlet, with the soundincreasing as more air is supplied. Largersize outlets generally are quieter at thesame air flow than smaller sizes of the same

model due to higher free area and/or lowerinlet velocity. Outlets should be selected sothat the resultant NC level does not exceedthe ASHRAE recommended values for theparticular space being considered.

Selection Fundamentals - Performance Factors

Figure 4: Air patterns

Circular Horizontal

Plan View Section View Section View Section View

Plenum Slot, 1 WayPlenum Slot, 2 WayVertical

Plan View Plan View Section View Section View

Sidewall Straight Floor 30° DeflectionFloor 0° DeflectionSidewall Spread

Plan View Plan View Plan View Plan View

Diffuser

Plan View

TerminalVelocityEnvelope

Throw

Spread

Angle of Discharge

Vertical Spread

Vertical Cross Section

Drop

Throw

Figure 5: Drop (left), spread (right)





Air Outlets

An important step in efficient space comfortconditioning is the proper selection of airoutlets. This section presents generalizeddescriptions and characteristics of thetypes of grilles, registers and diffusers com-monly used in commercial air distributionapplications today.

Grilles and RegistersThe term grille is commonly applied to anyair outlet or intake that consists of a squareor rectangular face and neck and whosefacial appearance is made up of stationaryor adjustable louvers which may be used todeflect the air.

A register is simply a grille which incorporatesan integral damper for air volume control.

Supply grilles and registers usually haveadjustable louvers and are available in singleor double deflection models.

The single deflection type includes oneset of blades in the horizontal or verticalorientation. Air pattern is adjustable in oneplane only.

The double deflection type includes twosets of blades in both the horizontaland vertical orientation (Figure 6), withair pattern being adjustable in both thehorizontal and vertical planes. Adjustmentof the vertical blades provides spreadcontrol of the air pattern, reducing boththrow and drop (Figure 3). Adjustment ofthe horizontal blades provides control over

the deflection of the air pattern (Figure 8).Air can be directed up or down to suit theapplication.

Supply grilles or registers are mostcommonly mounted in the sidewall within2 ft [610 mm] of a ceiling. Return grilles orregisters (Figure 7) usually have a fixedblade or core and can be located in thesidewall or ceiling.

Linear Bar GrilleThe linear bar grille is normally used wherean architectural blend of the grille to itssurroundings is required (Figure 9 andFigure 10). These grilles may be mountedin the sidewall, sill or floor, and may be usedfor supply or return. Louvers are fixed with

1/4 in. [6 mm] or 1/2 in. [13 mm] bar spacingand 0°, 15° or 30° deflection. See Figure11 and Figure 12 for mounting examples.

Linear Slot DiffuserLinear slot diffusers incorporate adjustablepattern controllers in a multi-slot configuration.Slot sizes are available in ½ in. [13 mm],¾ in. [19 mm] or 1 in. [25 mm] widths witha choice of one to ten slots. Adjustablepattern controllers allow horizontal left,horizontal right or vertical discharge formaximum flexibility. Typically used inceiling installations, the linear slot diffuser isarchitecturally appealing, particularly whensupplied in continuous lengths.

Figure 6: Double deflection supply grille Figure 7: Return grille

Figure 8: Upward deflection

20º Upward Deflection

Figure 9: Linear bar grille, 1/4 in.[6mm] spacing

Figure 10: Linear bar grille, 1/2 in.[13 mm] spacing

Figure 13: Linear slot diffuser

Figure 11: Sidewall application

Sidewall Application30º Upward Deflection

Figure 12: Sidewall application

Sill Application15º Deflection




Air Outlets

Round Ceiling Diffuser

Round ceiling diffusers consist of severalconcentric cones suspended below theceiling line by an outer cone (Figure 14).Neck sizes are available from 6 to 36 in.[152 to 914 mm], allowing a wide range ofair volume selections. Adjustable modelsare available to provide either horizontalor vertical air pattern. The round diffuser’sexcellent horizontal pattern makes it ideal forvariable air volume applications or exposedduct applications. Due to the availability oflarge neck sizes, the round ceiling diffuseris often used where high flow capacities arerequired (e.g. supermarkets, gymnasiums,halls, industrial applications).

Square Ceiling Diffuser

Square ceiling diffusers consist of severalconcentric square cones and a round neck(Figure 15). Air pattern is a uniform 360°horizontal pattern which is maintained atextremely low flows, making it ideal forvariable air volume applications. Sizes areavailable to suit standard ceiling modules12 in. x 12 in., 20 in. x 20 in., 24 in. x 24 in.[300 mm x 300 mm, 500 mm x 500 mm, 600mm x 600 mm]. Adjustable pattern modelsare available for horizontal or vertical airpattern setting.

Louver Face Diffuser

Louver face diffusers are available witha square or rectangular face composed

of a fixed modular core (Figure 16). Thismodular design allows for the selection of 1,2, 3 or 4 way air pattern. Available neck sizesare square or rectangular. In addition to thedesign flexibility, the louver face diffuser ispopular with architects because the louversdo not protrude below the ceiling line.

Round Plaque Diffuser

Round plaque diffusers consist of a plaquemounted inside an outer frame with a roundinlet (Figure 19). Standard round inlet sizesare available: 8 in. [203 mm], 10 in. [254mm], 12 in. [305 mm], and 14 in. [356 mm].There are three available field adjustableplaque positions that allow this diffuser togo from a fully horizontal throw to a fully

vertical throw. This adjustability makes thisdiffuser ideal for VAV as well as cooling andheating applications. The horizontal patternis discharged in a 360° circular pattern.

Square Plaque Diffusers

Square plaque diffusers are comprised ofa square plaque situated in a backpan witha round inlet (Figure 18). The air patternproduced is a uniform 360° circular patternwhich is maintained even at very lowvelocities, making it ideally suited for VAVsystems. Sizes are available to suit standardceiling modules: 12 in. x 12 in., 20 in. x 20in., 24 in. x 24 in. [300 mm x 300 mm, 500mm x 500 mm, 600 x 600 mm]. Panels arealso available to fit in different grid sizes.

Figure 14:Round ceiling diffuser

Figure 15:Square ceiling diffuser

Figure 16:Louvered face diffuser

Figure 17:Round plaque diffuser

Figure 18:Square plaque diffuser

Figure 19:Perforated ceiling diffuser

Perforated Ceiling Diffuser

Perforated ceiling diffusers are availablewith a square or rectangular face suppliedthrough a round or square neck (Figure19). Horizontal air pattern is achieved withdeflection vanes located at the diffuser faceor in the neck. The vanes can be configuredto achieve 1, 2, 3 or 4 way air pattern. Theperforated face blends in very well withthe acoustical tiles of typical suspendedceiling systems, and is therefore preferredby architects. Perforated return units (bothducted and non-ducted) are also availableto match the supply units.

Radial/Twist Diffusers

Radial/twist diffusers consist of a circularor square face with multiple air vanes,either fixed or adjustable, and a roundneck. Diffusers produce a horizontal orvertical twisting pattern for rapid mixing ofthe room air in heating or cooling modes.A distribution plenum or the outer conecan be connected directly to a round duct.Diffusers can be installed in a T-bar ceilingor exposed mounted to the ductwork.Adjustable air patterns can be manually,thermally or electronically controlleddepending on a room thermostat signal.Models are available for both commercialand industrial applications.

Plenum Slot Diffuser

These diffusers consist of a factoryfabricated plenum with integral patterncontrollers for vertical or horizontal airpattern adjustment. Plenum slot diffusersare easy to install as they are designedto lay-in on suspended ceiling grids. Thisfeature also provides flexibility for futuretenant revisions. Diffusers are available inlengths ranging from 2 ft to 5 ft [610 mmto 1524 mm] and offer a choice of multipleslot widths ranging from 1/2 in. [13 mm] to1½ in. [38 mm].

Light Troffer Diffuser

Light troffer diffusers are designed to

integrate with commercially availablelight fixtures in suspended ceiling systems(Figure 22).The troffer consists of a plenumsection, air slot and pattern controller.Troffers are available as single- or double-sided (saddle) units. Light troffer diffusersproduce an excellent horizontal air pattern,ideal for VAV applications. This is also themost efficient diffuser in terms of producingoptimum comfort conditions. Since the airslot is very narrow and integrated with thelight fixture, it is also appealing from anarchitectural standpoint.

Figure 20:Round Twist Diffuser

Figure 21:Plenum slot diffuser

Figure 22:Light troffer diffuser





Selection Procedures

Throw

Achieving the proper throw for a specific application is critical toproper outlet selection. Throw data is usually presented at terminalvelocities of 150 [0.75], 100 [0.50] and 50 fpm [0.25 m/s]. Generallyoutlets should be selected so that the throw at 50 fpm [0.25 m/s]terminal velocity equals the distance from the outlet to the boundaryof the conditioned space. In most cases this criteria will produceacceptable results.

When an air stream strikes a surface it tends to spread and followthe surface until the velocity dissipates. The total horizontal andvertical distance travelled by the air stream is equal to the tabulatedthrow of the outlet (Figure 23). For high ceiling applications it maybe desirable for the throw to exceed the space boundary (ceiling)and travel down the wall toward the occupied zone. However,penetration of the occupied zone should usually be avoided.

In addition to physical boundaries created by walls or partitions,boundaries can be created by the collision of two air patterns(Figure 24). Where two patterns will meet, the outlets should beselected so that the throw is equal to one half the distance betweenthe outlets. For high ceiling applications it may be desirable forthe throw to travel downward toward the occupied zone. Throwis again equal to the horizontal and vertical distance travelled bythe air stream.

It should be noted that most catalog throw data is presented forisothermal conditions (i.e., supply air temperature equals roomtemperature). During cooling the denser supply air will shorten thehorizontal throw to approximately 75% of tabulated values (multiplyby 0.75), assuming a temperature differential of approximately15 °F [7.5 °C].

The cataloged throw data for most diffusers and grilles is developedwith the outlet mounted in or adjacent to a ceiling. The ceiling orCoanda effect allows the supply air jet to be in contact with the

ceiling longer, reducing induction of room air and consequentlyresulting in a longer throw than if the outlet was mounted in freespace. If an air outlet is mounted in free space or more than 2 ft [610mm] from a surface, the cataloged throw data should be reduced byapproximately 30% (multiply by 0.70) (Figure 25 and Figure 26).

When selecting outlets for VAV application, both minimum andmaximum air quantities must be considered for throw. Althoughmany models of outlets provide excellent horizontal air pattern atextremely low flows, throws may be reduced below acceptablelimits.

In many applications it is desirable to limit the throw due to ceilinglayout, walls, partitions or other boundaries which may obstructthe air pattern and cause unacceptable velocities in the occupiedzone. There are several methods which may be used to minimizethrow from outlets, including spreading the air pattern, reducingair volume per inlet and selecting the appropriate air pattern.

More information on these methods will be presented on thefollowing pages.

Greater than18 in [457 mm]

Suspended Ceiling

Throw = A + B

A

B

Occupied Zone

A

B

Occupied Zone

Greater than2 ft [610 mm]

Suspended Ceiling

PRODUCT TIP

Slot diffusers and light troffer diffusers tend to maintainreasonable throws at low air volumes, and are thereforea good choice for VAV applications.

Figure 23: Throw of outlet

Figure 24: Boundaries created by two air patterns

Figure 25: Ceiling diffuser free space mounting

Figure 26: Sidewall outlet free space mounting



Spread

Spreading the air pattern dissipates the air stream over a widerarea and increases entrainment. This reduces the mass flow perunit surface area, which in turn reduces throw. Some outlets aredesigned to produce a spread pattern due to their geometry, whileothers such as supply grilles have adjustable vanes (Figure 27).Spreading the air is an effective way of reducing throw to avoid airpattern collisions with boundaries or other air jets.



Figure 27: Plan view of spread vs. throw

0°Deflection

22.5°Deflection

45°Deflection

15 ft [4.6 m]

14 ft [4.3 m]8 ft [2.4 m]

PRODUCT TIP

Some models of plenum slot diffusers and linear slotplenums are constructed with a sloped shoulder plenum.Thesloped plenum creates a natural spreading of the air pattern,substantially reducing the throw.

PRODUCT TIP

Some models of plenum slot diffusers and linear slot plenumsare constructed with a sloped shoulder plenum. The slopedplenum creates a natural spreading of the air pattern,substantially reducing the throw.

PRODUCT TIP

Louvered face supply grilles with adjustable blades provide ameasure of flexibility for the designer and building operatoras the throw and spread of the outlet can be field adjustedto account for changes in air volume, occupancy or ceilinglayout.

Air Volume

Throw is directly related to mass flow, therefore a reductionin air volume per outlet will reduce the throw. This can beachieved by utilizing more outlets with less air volumeper outlet. For linear diffusers or grilles, the same thing

can be achieved by dividing the outlet into active andinactive sections (Figure 29). Each active section handlesa smaller quantity of air, thereby reducing the throw. In order toeffectively separate the air pattern, the outlet should be divided byminimum inactive length (Table 1).

Air Pattern

The outlet air pattern has a large influence on the throw. 1 waypatterns tend to have the longest throw, while 4 way or roundpatterns have the shortest. The diffuser model will also affect thethrow. SeeTable 2 for a comparison of ceiling diffuser throw at equalair volume for various diffuser models and air patterns. The layoutof the ceiling and availability of installation location will determinethe optimum air pattern for the application.

Mapping

One method of selecting outlets based on throw is known as

'mapping.' The cataloged throw is referenced and corrected forcooling if conditioned air is supplied.The corrected throw is plottedon the reflected ceiling plan and checked for interference withobstructions, walls or other air jets.

Figure 28: Continuous grille

Figure 29: Active and inactive sections

Throw

Throw

Active/Inactive Sections

Length of Active Sections, ft [m] 1 [0.3] 5 [1.5] 10 [3]

Length of Inactive Sections, ft [m] 1 [0.3] 2 [0.6] 3 [0.9]

Table 1: Plan view of active and inactive sections

Diffuser Type Throw Distance, ft [m]

Square Cone 10 [3.0]

Round Cone 9 [2.7]

Perforated 4 way 14 [4.3]

Perforated 1 way 33 [10.1]

Modular Core 4 way 24 [7.3]

Modular Core 1 way 36 [11]

Table 2: Ceiling DiffuserThrow Comparison - 24 in. x 24 in. module[610 mm x 610 mm], 380 cfm, 700 fpm neck velocity, isothermalconditions, 50 fpm [0.25 m/s] terminal velocity





Example 1

A Model 520 size 6 in. x 5 in. supply grille operating at 150 cfm has been selected to supply a 10 ft x 15 ft room as illustrated in Figure 27What is the best deflection setting of the diffuser blades if conditioned cool air is supplied?

Referring to the catalog page we determine the 50 fpm throw to be :

0° deflection - 22 ft isothermal or (22 x .75) = 17 ft cooling



As seen from the pattern diagrams in Figure 25, the 22° deflection provides the best coverage and would be the optimum selection.

Supply Grille

15 ft

10 ft

SMALL OFFICE

9 ft

Performance Data - Model 520 Series, 6 in. x 5 in. Supply Grille

NC 20 30

Core Velocity, fpm 500 600 700 800 1000 1200

Velocity Pressure .016 .022 .030 .040 .062 .090

Size Total Pressure

0 .038 .052 .071 0.94 .146 .212

22½ .045 .063 .085 .114 .176 .256

45 .067 .093 .0126 .168 .261 .379

Ac =0.15 ft2

7 x 46 x 5

cfm 75 90 105 120 150 180

NC - - 15 19 26 31

Throw, ft

0 7-10-16 8-12-17 9-13-19 11-14-20 13-16-22 14-17-24

22½ 6-8-13 6-10-14 7-10-15 9-11-16 10-13-18 11-14-19

45 3-5-8 4-6-9 5-7-9 5-7-10 6-8-11 7-9-12

Table 3: Model 520 series, 6 in. x 5 in. supply grille performance data





ADPI

Extensive studies have resulted inrelationships between local temperatures,velocities and comfort reactions. On thebasis of the temperature and velocity at aspecific point, an effective draft temperaturecan be calculated for that location. The drafttemperature is calculated by the equation:

ϴed = (T x - T c ) - 8(V x - 0.15) Eq.1

where:

ϴ = draft temperature

T x = local temperature

T c = control temperature

V x = local velocity

Research indicates that a high percentage ofpeople are comfortable when the effectivedraft temperature difference is between -3 °F[-2 °C] and +2 °F [+1 °C] and the air velocityis less than 70 fpm [0.36 m/s]. This comfortzone is illustrated as the shaded area inFigure 30.

Using this draft temperature as our criteria,the quality of room air diffusion can bedetermined based on the Air DiffusionPerformance Index (ADPI). ADPI is definedas the percentage of locations in theoccupied space which meet the comfortcriteria based on velocity and temperature

measurements taken at a given numberof uniformly distributed points. This ADPIvalue has proven to be a valid measure ofan air diffusion system.

The ADPI rating of an air diffusion systemdepends on a number of factors:

• Outlet type

• Room dimensions and diffuser layout

• Room load

• Outlet throw

When properly selected, most outlets canachieve an acceptable ADPI rating.

The higher the ADPI rating, the higher thequality of room air diffusion within thespace. Generally an ADPI of 80 is consideredacceptable.

Through extensive testing, relationshipshave been developed between ADPIand the ratio of throw over characteristiclength (T/L). Throw is the isothermalthrow at a selected terminal velocity takenfrom catalog performance charts. Thecharacteristic length is the distance fromthe outlet to the nearest boundary. Table4 provides definition of characteristic lengthfor various outlet types. See Figure 31 forfurther clarification.

Figure 30: Comfort criteria - draft temperature

Local Air Temp. - Ambient Temp., ̊ F (T - T c )˚ F

Local Air Temp. - Ambient Temp., ̊ F (T - T c )˚C

-5 5-4 4-3 3-2 2-1 10

-2.5 2.5-2 2-1.5 1.5-1 1-0.5 0.50

10

0

20

30

40

50

60

70

80

0.05

0

0.10

0.15

0.20

0.25

0.30

0.35

0.04

V e l

o c i t y ,

f p m

V e l

o c i t y ,

m / s

ɵ = - 3

ɵ = 0

ɵ = 2

Diffuser Type Characteristic Length, L

High Sidewall Grille Distance to wall perpendicular to jet

Circular Ceiling Diffuser Distance to closest wall or intersecting air jet

Sill Grille Length of room in the direction of the jet flow

Ceiling Slot Diffuser Distance to wall or midplane between outlets

Light Troffer DiffusersDistance to midplane between outlets, plusdistance from ceiling to top of occupied zone

Perforated, Louvered CeilingDiffusers Distance to wall or midplane between outlets

It should be noted that Table 4 is based on a standard 9 ft [2.7 m] ceiling height. For roomswith ceiling heights lower or higher, the characteristic length should be corrected downor up by the difference from 9 ft [2.7 m].

For example, a 20 ft [6.1 m] long room with a 12 ft [3.7 m] ceiling height and high sidewallgrille:

Distance from grille to perpendicular wall = 20 ft [6.1 m], height correction: 12 - 9 = 3 ft(3.7 - 2.7 = 1 m] , characteristic length: 20 + 3 = 23 ft [6.1 + 1 = 7.1 m].

Note that the ADPI is applicable only for cooling mode conditions and can be field or labmeasured using the test method described in ASHRAE Standard 113.

Table 4: Characteristic length for various diffuser types






Heating mode conditions can be evaluatedusing ASHRAE Standard 55 guidelines andthe test method of ASHRAE Standard 113.

Table 5 illustrates the range of T/L valueswhich will result in optimum ADPI values forvarious outlet types at several room loads.By selecting a throw from the catalog datawhich produces the required T/L ratios, anacceptable ADPI rating can be achieved.

By studying Table 5, we can make severalobservations which are valuable to considerwhen selecting air outlets for maximumADPI:

1. Generally, the higher the room load,the more difficult it is to achieve a high

ADPI.2. A value of T/L = 1.0 generally will

produce an acceptable ADPI.

3. Some air outlets are better than others atachieving high ADPI values. For example,a sidewall grille has a maximum ADPI valueof 85, while the circular ceiling diffusercan achieve an ADPI value of 93.

4. A wideT/L range allows the designer moreflexibility in selecting the air outlet foroptimum ADPI.

5. Outlets with a wide T/L range are moreapplicable to VAV systems as theycan maintain a high ADPI even whenturned down to low air volume. At 20Btu/h/ft2 [63 W/m2] a ceiling slot diffuser

has a turn-down ratio of 20% whilemaintaining an ADPI of greater than 80.At the same condition the high sidewallgrille has a turn-down ratio of approximately50%. Light troffer diffusers have the largestT/L range of all outlets, making them anexcellent choice for VAV applications.

Figure 31: Characteristic length illustration

High Sidewall Grill

L

L L

L L L

Ceiling and Slot Diffusers

Sill Grill Light Troffer Diffusers

Occupied Zone

L L

Terminal DeviceRoom Load

W/m2

T0.25/Lfor Max.

ADPI

Max.ADPI

ADPIGreater

Than

Range ofT0.25/L

High Sidewall Grilles

250 1.8 68 - -

190 1.8 72 70 1.5 to 2.2

125 1.6 78 70 1.2 to 2.3

65 1.5 85 80 1.0 to 1.9

< 30 1.4 90 80 0.7 to 2.1

Circular Ceiling

Diffusers*

250 0.8 76 70 0.7 to 1.3

190 0.8 83 80 0.7 to 1.2

125 0.8 88 80 0.5 to 1.5

65 0.8 93 80 0.4 to 1.7

< 30 0.8 99 80 0.4 to 1.7

Sill Grille

Straight Vanes

250 1.7 61 60 1.5 to 1.7

190 1.7 72 70 1.4 to 1.7

125 1.3 86 80 1.2 to 1.8

65 0.9 95 90 0.8 to 1.3

Sill Grille

Spread Vanes

250 0.7 94 90 0.6 to 1.5

190 0.7 94 80 0.6 to 1.7

125 0.7 94 - -

65 0.7 94 - -

Ceiling Slot Diffusers

(for T100 /L)

250 0.3 85 80 0.3 to 0.7

190 0.3 88 80 0.3 to 0.8

125 0.3 91 80 0.3 to 1.1

65 0.3 92 80 0.3 to 1.5

Light Troffer Diffusers

190 2.5 86 80 < 3.8

125 1.0 92 90 < 3.0

65 1.0 95 90 < 4.5

Perforated & LouveredCeiling Diffusers

35 to 160 2.0 96 90 1.4 to 2.7

35 to 160 2.0 96 80 1.0 to 3.4*Includes square cone diffusers and square plaque diffusers

Table 5: Air diffusion performance index (ADPI) selection guide

ALL-IN-ONE TIP

Price All-In-One selection softwareincludes an ADPI calculation tool forautomated calculation of ADPI forall outlet models.

PRODUCT TIP

Although not fully supported byresearch it is generally acceptedthat a high ADPI rating will producea correspondingly high ventilationeffectiveness, (i.e. approaching 1.0).If the supply air is well mixed andevenly distributed in the space,then any contaminants will alsobe evenly distributed, providingmaximum indoor air quality.





VAV Applications

When selecting air outlets for VAV applications it is important to analyzethe ADPI at both the maximum and reduced flow conditions. Formost outlets the throw, and consequently the T/L ratio, drops off asthe air flow through the diffuser is decreased. If the T/L ratio dropstoo low ADPI can be compromised. Selecting an outlet for highADPI at maximum flow does not ensure acceptable air distributionin the space when the load is reduced. Since ADPI is a measure ofthe air diffusion quality in the space, we are not concerned withthe ADPI value when the space is unoccupied with the air outletat minimum volume. We should, however, review the selection atlow load conditions, such as when occupancy is reduced and/orexternal loads are at minimum.

Refer to Chapter 9—Mixing Ventilation in the Price Engineer's HVACHandbook for examples that provide a step-by-step procedure forselection of air outlets using ADPI.

Pressure DropSupply air outlets produce both a static pressure loss and a velocitypressure loss. The static pressure loss is equal to the differencebetween the inlet static pressure (SPi) and the room pressure(usually atmospheric). The static pressure loss is dependent onoutlet geometry and/or free area and must be derived by test. Staticpressure loss is directly proportional to the volume of air suppliedthrough the outlet. The velocity pressure loss is equal to the velocitypressure at the inlet (VPi) and the room velocity pressure (zero).See Figure 32 and Figure 33.

The inlet velocity, and subsequently the velocity pressure loss, canbe calculated from equations 2 and 3. The total pressure loss of anoutlet is equal to the sum of the static and velocity pressure losses(equation 4).

Most catalog data lists the total pressure loss for a given air volume.If velocity pressure is provided, the static pressure can be derived

from equation 4; however, if velocity pressure is not provided, itcan be calculated based on the inlet velocity. For ceiling diffusersand plenum slot diffusers the inlet velocity is based on the inletarea. For sidewall grilles and registers the inlet velocity is basedon the grille core area.

Velocity Eq.2

Velocity Pressure Eq.3

Total Pressure Eq.4

SPi

VPi

SPi

VPi

Figure 32: Ceiling diffuser

Figure 33: Slot diffuser





Example 2

A model SDB 100 2 slot, 60 in. diffuser with8 in. round inlet is selected for 280 cfm. Whatis the pressure loss?

From Table 6 performance data, the totalpressure = 0.122 in. w.g. at 280 cfm.

Neck Area Eq.5

Neck Velocity Eq.6

Velocity Pressure Eq.7

Static Pressure Eq.8

Performance Data - Model SDB 100, 2-slot, 60 in. diffuser - 8 in. Round Inlet

Capacity, cfm 160 190 220 250 280 310

36 in.

(6 in.

Inlet)

Projection, ft H 7-14-20 11-15-22 13-16-23 14-17-24 15-19-26 16-19-27

V 17 19 21 23 24 25

Tp 0.122 0.171 0.229 0.293 0.368 0.452

NC 24 29 34 37 41 44

48 in.

(7 in.

Inlet)

Projection, ft H 5-13-20 7-16-23 10-17-24 12-18-26 16-19-28 17-20-29

V 17 19 22 23 24 26

Tp 0.060 0.087 0.114 0.150 0.188 0.228

NC - - 23 27 30 33

60 in.

(8 in.

Inlet)

Projection, ft H 4-9-20 5-14-22 7-17-23 9-18-25 10-20-26 13-20-29

V 14 17 20 22 23 25

Tp 0.040 0.055 0.076 0.098 0.122 0.149

NC - - - 21 24 27

Table 6: Model SDB 100, 2-slot, 60 in. diffuser - 8 in. round inlet performance data





Diffuser Type NC Level

Square Cone 17

Square Plaque 18

Round Cone 22

Modular Core 26

Perforated Curved Vane 28

Louvered Face 31

Perforated Face Deflector 33

Perforated Neck Deflector 37

Noise Criteria

The first step in selection of an air outletis defining the actual model type. Alarge variety of outlet styles, shapes andconfigurations are available. In many casesthe outlet model selection is based onarchitectural or economic considerations.This decision on outlet type or modelhas significant influence on the resultantnoise levels of the application since noisegeneration of air outlets depends ontheir design and geometry. Outlets withaerodynamic components and high freearea will generally have lower noise levelsat the same air flow.

Table 7 lists the NC level for several ceiling

diffusers at the same air volume and neckvelocity. The resultant NC level varies froma barely perceptible NC 17 for the squarecone to a marginally acceptable NC 37 forthe PDN. The table illustrates several pointsto consider when selecting air outlets.

1. The square plaque and square conediffuser are an excellent choice foracoustically sensitive applications orwhen high air volumes per outlet aredesired. This is due to the aerodynamiccones and high free area.

2. Perforated diffusers tend to be noisier thanother available models at the same airvolume. This is due to the restricted freearea of the perforated face and patterndeflectors in the air stream.

3. There is a fairly large variation in generatednoise levels, even between variousperforated diffuser types. The curvedpattern controllers of the perforated curveddiffuser generates less sound than theless aerodynamic neck deflectors of theperforated neck deflector diffuser.

4. Selecting outlets based on neckvelocity is a poor indication of acousticperformance.

5. To ensure predictable sound levels it isessential to reference the manufacturers’cataloged sound levels for the specifiedproduct.

Table 8 illustrates a similar noise levelcomparison for several models of plenumslot diffusers selected at the sameconditions. Again, a wide range of acousticperformance is seen as a result of thediffuser design. The linear slot diffuser canbe seen as the obvious choice for highcapacity, noise-sensitive applications.

Table 7: Diffuser sound comparison - 24 in. x 24 in. module [610 mm x 610 mm], 380 cfm[180 L/s], 700 fpm [3.6 m/s] neck velocity

Diffuser Type NC Level

Linear Slot 31

Linear Fixed Curved 36

Linear Ice Tong 39

Linear Wiper Blade 46

Table 8: Plenum slot diffuser sound comparison - 1 in. slot, 4 ft [1.2 m], 270 cfm [127 L/s],8 in. [203 mm] neck, 800 fpm [4.1 m/s] neck velocity




Guidelines to Minimize Noise in an AirDistribution System

• Size the ductwork and duct elements forlow air velocity.

• Avoid abrupt changes in duct cross-sectional area or direction.

• Provide smooth air ow atall duct elements, includingbranches, elbows, transitionsand air outlets.

• When exible duct is used it should bepulled taught and installed as straight aspossible.

• Provide straight ductwork (preferablyfive to ten duct diameters) between duct

elements. • Use equalizing grids when non ideal

inlets cannot be avoided.

• Balance the duct system for lowest reasonable fan speed with dampersgenerally open.

• Locate volume control dampers aminimum of three (preferably fiveto ten) duct diameters away from airoutlets.

Selection ProcedureTable 9 illustrates the ASHRAE recommendedspace NC values for many commercial airconditioning applications. Outlets should beselected so that the tabulated NC levels arewithin these design goals.

Refer to Chapter 9—Mixing Ventilation in thePrice Engineer's HVAC Handbook for noiseselection procedures and examples.

Room Types RC / NC

Private Residences 25-35

Hotels/Motels

Individual rooms or suites 25-35

Meeting/banquet rooms 25-35

Corridors, lobbies 35-45

Service/support areas 35-45

Office Buildings

Executive and private offices 25-35

Conference rooms 25-35

Teleconference rooms < 25

Open-plan offices < 40

- With sound masking < 35 Corridors and lobbies 40-45

Hospitals and Clinics

Private rooms 25-35

Wards 30-40

Operating rooms 25-35

Corridors and public areas 30-45

Performing Arts Spaces c

Drama theaters 25

Music teaching studios 25

Music practice rooms 30-35

Schools d

Classrooms 25-30

Large lecture rooms 25-30

Large lecture rooms, without speech amplification 25Laboratories (with Fume Hoods)

Testing/research, minimal speech communication 45-55

Research, extensive telephone use, speech communication 40-50

Group teaching 35-45

Church, Mosque, Synagogue

General assembly 25-35

With critical music programs c

Libraries 30-40

Courtrooms

Un-amplified speech 25-35

Amplified speech 30-40

Indoor Stadiums, Gymnasiums

Gymnasiums and natatoriumse 40-50

Large seating-capacity spaces with speech amplificatione

45-55

Table 9: Design guidelines for HVAC system noise in unoccupied spaces



a The values and ranges are based on judgment and experience, not quantitative evaluations of human reactions

They represent general limits of acceptability for typical building occupancies. Higher or lower values may be

appropriate and should be based on a careful analysis of economics, space use and user needs.

bWhen quality of sound in the space is important, specify criteria in terms of RC(N). If the quality of the sound in

the space is of secondary concern, the criteria may be specified in terms of NC or NCB levels of similar magnitude

c An experienced acoustical consultant should be retained for guidance on acoustically critical spaces (below

RC 30) and for all performing arts spaces.

d Some educators and others believe that HVAC-related sound criteria for schools, as listed in previous editions

of this table, are too high and impede learning for affected groups of all ages. See ANSI Standard S12.60-2002

for classroom acoustics and a justification for lower sound criteria in schools. The HVAC component of tota

noise meets the background noise requirement of that standard if HVAC-related background sound is RC 25(N)

e RC or NC criteria for these spaces need only be selected for the desired speech.

Reference • 2007 ASHRAE Applications Handbook, Table 42, page 47.34

• AHRI Standard 885-2008, Table 15, page 31



S u p p l y A

i r

Cold Primary Air

1

2

3

4

6

5

1

2

3

4

5

6


Low Temperature Systems

Description

Low temperature air distribution systemstypically supply conditioned air at nominaltemperatures of between 42 °F [6 °C] and47 °F [8 °C], as compared to conventionalsystems which supply air at temperaturesbetween 55 °F [13 °C] and 59 °F [15 °C]. Lowtemperature air distribution systems havebeen applied mainly in conjunction with icestorage systems to take advantage of thelow temperature chilled water produced bythese systems.

Ice storage systems have been appliedto reduce electrical demand during peakperiods. Electric chillers are used to freezewater at night when utility rates are low.

During the day the ice is used to cool thebuilding, reducing operation of the electricchiller during peak periods. Electric utilitiesin some areas also offer incentives to ownersinstalling ice storage systems.

Design Considerations

Several design considerations must betaken into account when considering a lowtemperature air distribution system. Somecommon concerns include condensation,comfort and indoor air quality.

Low Temperature Air Outlets

If low temperature air is to be supplieddirectly to the space, supply air outletsmust be designed and tested to provide

good mixing and maintain a horizontal airpattern at low flow conditions. In addition,the diffuser must be properly insulatedand sealed to prevent condensation fromforming on the diffuser surface.

Low temperature air outlets have beendeveloped specifically for the supply oflow temperature air. All outlets featurehigh induction jets which rapidly mix supplyand room air as well as maintain a goodhorizontal air pattern at low flow conditions.These features ensure comfort conditionsare provided in the space.

When supplying low temperature airdirectly to the space, the terminal unit andaccessories such as reheat coils, attenuators,etc., must also be specifically constructed to

prevent condensation.

Variable Volume Supply with LowTemperature Air Outlets

Some manufacturers have developedvarious air distribution components whichcan provide a supply of low temperature airto the space while maintaining comfortableconditions under variable air volumeoperation.

Figure 35 presents various low temperaturediffuser options utilized in conjunction witha single duct VAV reheat terminal designedfor low temperature operation.

PRODUCT TIP

Low temperature outlets are availablewith cataloged performance dataat reduced supply air temperature,ensuring proper selection.

Linear Outlet Swirl Outlet

Supply Air Induced Room Air

Figure 34: Low temperature air outlets

Figure 35: Variable volume supply with low temperature air outlets

1. Low Temperature Perforated Face Diffuser

• Induction chamber aids rapid mixingof low temperature air.

• Aerodynamic shape of backpanensures excellent horizontal air pattern.

• Perforated face blends well withsuspended ceiling tiles.

• Factory insulated and sealed to preventcondensation.

2. Hot Water Coil

• Factory insulated and sealed with external foil faced insulation to prevent

condensation. • Available with insulated access door.

• One or two row coils available.

3. Single Duct Terminal with LowTemperature Supply Option


• Isolated and insulated inlet duct foilfaced internal insulation.

4. Low Temperature Linear Diffuser


• 1 or 2 way horizontal air pattern.


PRODUCT TIP

Low temperature construction forsingle duct terminals include internalvapor barrier, thermally isolated inletvalves and insulated inlet collar.

5. Low Temperature Square Plaque Diffuser


• Flush face of plaque provides architecturalappeal.


• Aerodynamic shape of backpanensures excellent horizontal air pattern.

6. Low Temperature Radial Vane Diffuser

• High induction vortex air pattern providesrapid mixing of low temperature air.






Industrial Ventilation

The purpose of an industrial ventilationsystem is to reduce the exposure to excessheat and contaminants generated in anindustrial environment. The most effectivemethod of removing excess heat andcontaminants is at the source with a localexhaust system. Another method is dilutionwith general ventilation by either a fansystem, natural draft or a combination ofthe two. In some cases cooling is required tomaintain acceptable space conditions, eitherfor people or processes. Many industrialapplications require a combination of localexhaust, general ventilation supply andgeneral exhaust to handle simultaneousremoval of heat and contaminants. This

section will focus on general ventilationsupply air systems.

Air Supply Methods

Similar to commercial spaces, there areseveral methods of supplying air to anindustrial space. The following are the mostcommon:

Mixing Air Distribution

Supply air exits the outlet at a high velocity,inducing room air to provide mixing andtemperature equalization before the air jetreaches the occupied zone. Since the air jetinduces the surrounding air, the contaminantconcentration in the space is diluted.

Displacement Ventilation

Introduces air into the space at low velocities,which causes minimal induction and mixing.Displacement outlets may be located almostanywhere within the space, but have beentraditionally located at or near floor level.Thesystem utilizes buoyancy forces generatedby heat sources such as people or processesto remove contaminants and heat from theoccupied zone. See Volume 4, Section J forDisplacement Ventilation Outlets.

Localized Ventilation

Introduces the air directly to a specific area ofa space or toward the breathing zone of anoccupant to provide comfort conditions and/orcontrol of contaminants.The close proximity ofthe outlet to the source prevents entrainmentof contaminants, providing a much cleaner

work area than the surrounding space.

Unidirectional or Plug Flow

Introduces non turbulent or laminar supplyair to the space to control contaminants andobtain a high level of cleanliness.

Air Outlets

Due to the unique and extreme conditionsexperienced in the industrial environment,specific air outlet models have beendeveloped for this application. Several arepresented below:

Industrial Supply Grilles and Registers

Similar to commercial models, the grilleor register has adjustable louvers in

single or double deflection; however, thelouvers are deeper (up to 3 in. [76 mm])and spaced wider. The deeper louver isstronger and more effective for patterndeflection. Construction is generallyextruded aluminum louvers and heavyduty aluminum or steel frame. The heavyduty construction of the industrial supplygrilles and registers withstands frequentadjustment, high velocity and air volumes,

turbulent supply air, and contaminants in theair stream. Options include gang operators,quick-release trunk latch frame and heavyduty balancing damper (Figure 36).

Drum Louver

Drum louvers consist of adjustable vanesmounted in a rotating drum which isadjustable up or down to provide directionalcontrol of the air pattern.The deep adjustablevanes can be used to achieve varyingamounts of spread pattern. The depth ofthe drum and vanes produces a long airprojection and high degree of directionalcontrol. Construction can be heavy gaugesteel or extruded aluminum. Options includepole operator bracket, motorized drum andheavy duty balancing damper (Figure 37).

Nozzle

Similar to the drum louver, the nozzleachieves a very long air projection due toits depth and geometry. Generally round inshape, nozzles are available in a variety ofmodels including adjustable versions whichallow directional control of the air pattern.Construction can be steel or aluminum.Options include motorized direction controland twist elements for throw and spreadadjustment (Figure 38).

Industrial Return Grilles or Registers

Grilles or registers have fixed blades ofvarious deflection and blade spacing and areconstructed of heavy gauge steel or extruded

aluminum with welded frame. Optionsinclude stainless steel construction and heavyduty balancing damper (Figure 39).

Security Grilles

Due to their heavy duty construction, securitygrilles are a good option for severe industriaenvironments in addition to institutionaapplications (Figure 40).

Construction Features

When selecting outlets for industriaapplications there are several constructionand functional features to consider. Supplygrilles or nozzles should include a meansof adjusting the direction of air flow tofacilitate changes to the work area layouor changes due to seasonal variations. Onmulti-blade grilles a gang operator optionsimplifies blade adjustment. Often the aioutlets are subjected to high velocities andturbulent flow conditions. Vibration of theductwork due to close coupled fans or otheequipment can also be present. To prevengrille blades or the nozzle drum from movingunder the influence of these conditions, alocking mechanism is recommended.

Other options to consider are:

• Quick-release fastening frame for easyremoval and replacement for cleaning

• Filter frame for return grilles

• Stainless steel construction for corrosiveenvironments

• Heavy duty industrial grade balancingdampers with locking mechanism

• Heavy duty gym grilles or securitygrilles for return applications to prevendamage in low areas

Air Outlet Selection

Refer to Chapter 9—Mixing Ventilation in thePrice Engineer's HVAC Handbook for IndustriaOutlet selection procedures and examples.

Figure 36:Industrial supply grille

Figure 37: Drum louver Figure 38: Nozzle

Figure 39:Industrial return grille

Figure 40:Security grille



The conversion data presented in thiscatalog is based on the following referencestandards:

1. National Standard of Canada, “MetricPractice Guide" CAN3-Z234. 1-76(Canadian Standards Association, 178Rexdale Boulevard, Rexdale, Ontario

M9N 1R3).2. “ASHRAE SI Metric Guide for Heating,

Refrigerating, Ventilating, and AirConditioning” (ASHRAE Inc., 1791 TullieCircle, NE, Atlanta, Georgia, 30329.

3. “Supplementary Metric Practice Guidefor Heating, Ventilating, Air Con-ditioning, Refrigeration, Plumbingand Air Pollution Equipment Manu-facturing Industries” (Heating,Refrigerating and Air ConditioningInstitute of Canada; 385 The WestMall, Suite 267, Etobicoke, OntarioM9C 1E7)

Temperature

1. To convert from degree Fahrenheit todegree Celsius, subtract 32 and divideby 1.8.

2. To convert from degree Celsius to degreeFahrenheit, multiply by 1.8 and add 32.

3. To convert from degree Fahrenheit toKelvin, add 459.67 and divide by 1.8.

4. To convert from Kelvin to degreeFahrenheit, multiply by 1.8 and subtract459.67.

5. To convert from degree Celsius to Kelvin,add 273.15.

6. To convert from Kelvin to degree Celsius,subtract 273.15.

7. To convert from degree Rankin to Kelvin,divide by 1.8.

Conversion Factors

Item To Convert From To SI Units Multiply ByImperial Units

Length inches millimetres mm 25.4

inches metres m 0.0254feet metres m 0.3048

Area square inches square millimetres mm2 645.16

square inches square centimetres cm2 6.4516square inches square metres m2 0.000 645 16square feet square metres m2 0.092 903 04

Volume — Air std. cubic feet per minute cubic metres per second m3 /s 0.000 471 947Flow std. cubic feet per minute cubic metres per hour m3 /h 1.699

std. cubic feet per minute litres per second L/s 0.471 947

Under 1m3 /s use L/s

Volume — Liquid gallon (Can.) litre L 4.546 090

& Liquid Flow gallon (U.S.) liter L 3.785 412gallons per minute (Can.) litre per second L/s 0.075 768gallons per minute (U.S.) liter per second L/s 0.063 09gallons per hour (Can.) litre per second L/s 0.001 263

gallons per hour (U.S.) liter per second L/s 0.001 051

Velocity feet per second metres per second m/s 0.3048

feet per minute metres per second m/s 0.005 080

Pressure inches of water (60 °F) pascal (20 °C) Pa 248.84foot of water (39.2 °F) pascal (20 °C) Pa 2 988.98

inches of mercury (60 °F) pascal Pa 3 376.85lb force per square inch (psi) pascal Pa 6 894.757lb force per square foot pascal Pa 48.880 26

Energy btu joule J 1 055.056

Power Horsepower watt W 746kilowatts KW 0.746

Temperature Rankin kelvin K 5/9(see next page) Fahrenheit Celsius, Centigrade C (F-32) (5/9)

Heat flow rate btu per hour watt W 0.293 071kilowatt KW 0.000 293 071

Weight ounce gram g 28.350

pound kilogram kg 0.4536

Density pounds per kilograms per kg/m3 16.018cubic foot cubic meter kg/m3

Example

A) Grilles & Registers

Price 20 in. x 4 in. 22/C/S at 550 cfm,0.156 in. w.g. total pressure, corevelocity = 1200 fpm will be described inSI units as follows:

Price 508 mm x 102 mm, 22/C/S at 275L/s. 39 Pa total pressure, core velocity= 6 m/s.

B) Diffusers

Price 24 in. x 24 in., 10 in. round inletSCD at 490 cfm, .098 in. w.g. totalpressure neck velocity = 900 fpm will bedescribed in SI units as follows:

Price 600 mm x 600 mm, 250 mm roundinlet SCD at 231 L/s, 25 Pa total pressure,neck velocity = 5 m/s.

Note:

Dimensions are 'soft' conversion, androunded to the nearest millimetre.



http://slidepdf.com/reader/full/air-distribution-engineering-guide 19/19

References


ACGIH (2004). Industrial ventilation manual of recommended practice.

AHRI. Standard 855—Procedure for estimating occupied space sound levels in the application of air terminals and

air outlets.

ASHRAE (1991). Chapter 42. ASHRAE handbook—HVAC applications. Atlanta, GA: American Society of Heating,

Refrigeration, Air-Conditioning Engineers.







ASHRAE (2009). Chapter 8.ASHRAE handbook—Fundamentals. Atlanta, GA: American Society of Heating, Refrigeration,

Air-Conditioning Engineers.

ASHRAE (2009). Chapter 20.ASHRAE handbook—Fundamentals. Atlanta, GA: American Society of Heating, Refrigeration,

Air-Conditioning Engineers.

Kirkpatrick, A. T., & Elleson, J. S. (1996). Cold air distribution system design guide. Atlanta, GA: American Society of

Heating, Refrigeration and Air-Conditioning Engineers.

Nevins, R. G. (1976).Air diffusion dynamics, theory, design and application. Birmingham, MI: Business News Publishing

Company.

Documents

Air Distribution Engineering Guide